High temperature superconducting thin film structures produced by current fabrication methods have deposited the high temperature superconducting thin film directly onto a suitable single crystal substrate such as strontium titanate, yttria-stabilized zirconia, alumina or magnesium oxide (periclase), or have used a barrier layer such as Ag, Pt, Nb, ZrO.sub.2, etc., to separate the superconductor from the substrate. None of the currently employed buffer layers have been lattice matched to the substrate. Thus, in the absence of the buffer layer, the film may react with the substrate, allowing diffusion of the constituent species from the substrate into the superconducting film or from the film into the substrate, either of which resulting in the modification of the properties of the superconductor. With a buffer layer which has not been lattice matched to the substrate, optimization of the crystalline perfection of the superconducting film is impeded.